Having enough classrooms to accommodate all your students sounds basic, but an international survey shows that almost one in 10 schools in developed nations do not have sufficient room.
The figures from last month's Programme for International Student Assessment (Pisa) results show that on average 8.9 per cent of school leaders in richer countries say that a shortage of adequate classroom space is hindering learning in their school. This ranges from just 2.2 per cent of school leaders in Iceland to 19.1 per cent in Luxembourg.
The Organisation for Economic Cooperation and Development (OECD), which runs Pisa, asked school leaders to report on the state of their buildings overall, on heating, cooling and lighting systems, and on classroom space.
"While an adequate physical infrastructure and supply of educational resources does not guarantee good learning outcomes, the absence of such resources could negatively affect learning," the Pisa report says.
In the UK, population growth is putting increasing pressure on schools to provide more space. The government recently announced that it would be putting an extra #163;2.35 billion into creating more places up to 2017, in addition to the #163;5 billion already allocated since 2011.
Department for Education statistics show that there will be 4.79 million children in primary schools by 2022 - 15 per cent more than in 2013.
AROUND THE WORLD
Percentage of students in schools whose headteachers report that lack of classroom space does not hinder teaching
Hong Kong, China 65
Republic of Ireland 61
Shanghai, China 58
South Korea 53